Implementation, demonstration and validation of a user-defined wall-function for direct precipitation fouling in ANSYS Fluent

In a previous paper (Johnsen et al., 2015) and presentation (Johnsen et al., 2016), we developed and demonstrated a generic modelling framework for the modelling of direct precipitation fouling from multi-component fluid mixtures that become super-saturated at the wall. The modelling concept involves the 1-dimensional transport of the fluid species through the turbulent boundary layer close to the wall. The governing equations include the Reynolds-averaged (RANS) advection-diffusion equations for each fluid species, and the axial momentum and energy equations for the fluid mixture. The driving force for the diffusive transport is the local gradient in the species' chemical potential. Adsorption mechanisms are not modelled per se, but the time-scale of adsorption is reflected in the choice of Dirichlet boundary conditions for the depositing species, at the fluid-solid interface. In this paper, the modelling framework is implemented as a user-defined function (UDF) for the CFD software ANSYS Fluent, to act as a wall boundary condition for mass-transfer to the wall. The subgrid, 1-dimensional formulation of the model reduces the computational cost associated with resolving the fine length-scales at which the boundary-layer mass transfer is determined, and allows for efficient modelling of industry-scale heat exchangers suffering from fouling. The current paper describes the modelling framework, and demonstrates and validates its applicability in a simplified 2D heat exchanger geometry (experimental and detailed CFD modelling data by P\"a\"akk\"onen et al. (2012, 2016)). By tuning the diffusivity, only, good agreement with the experimental data and the detailed CFD model was obtained, in terms of area-averaged deposition rates.Comment: 12th International Conference on CFD in Oil & Gas, Metallurgical and Process Industries, SINTEF, Trondheim, NORWAY, May 30th - June 1st, 2017, 9 pages, 9 figure

Demonstration of a novel instrument for online monitoring of absorber emissions to air

A novel concept for online monitoring of nitrosamines, solvent amines and their degradation products in amine absorber emissions to air was demonstrated at the Tiller CO2-lab pilot facility. The monitoring concept is based on SINTEF patent No. PCT/EP2011/073557. The measurement method applies gas sampling by capture of analytes in a condensate stream from a single stage condensate collector unit. An improved design for the SINTEF prototype for online gas and liquid measurements has been established as part of the CCUS-ALIGN project. The new design has low complexity and improved robustness, making it applicable as integrated part of industrial monitoring systems. The established prototype was successfully tested for monitoring of trace gas emission from a CO2 capture pilot plant, demonstrating measurements of nitrosamines at levels far below the lower detection limits of commercial industrial online analyzers. Results from testing of a condensate collector prototype indicate high capture efficiency for analytes of interest, including analytes present in aerosols during operation conditions where the absorber emit mist to the atmosphere. The measurement concept has potential for significantly reducing the costs related to manual gas measurements for critical trace gas components in plant operation. Application of the concept can enable continuous measurements of nitrosamines and other critical trace gas analytes in the emissions to air not currently available in absorption-based CO2 capture processes.publishedVersio

Modeling the Growth of Clostridium beijerinckii NCIMB 8052 on Lignocellulosic Sugars

To our knowledge, this is the first growth model of Clostridium beijerinckii NCIMB 8052 on glucose and xylose as representative lignocellulosic sugars, which considers the synergistic effects of sugars on the growth rate. We fitted models with different types of interactions between the substrates to the growth rate data obtained with varying sugar concentrations. Noncompetitive binary substrate growth model gave the best fit with the smallest mean standard errors (MSE), and sum of squares error (SSE), 0.0778 and 0.0071, respectively. Confidence intervals for the parameter estimates showed that the substrate affinity constant for xylose, KsX (g/l) had the largest uncertainty, while the maximum specific growth rate on xylose, µmaxX (h-1) had the smallest. The correlation matrix showed that the model parameters were highly correlated. Carbon cataboliterepression (CCR) effect on the growth rate was of the noncompetitive type. Validation with other sugar concentration values is necessary to evaluate the prediction capability of the proposed model. A transcriptional study will be beneficial to understand global gene regulation mechanisms as guidance for improving the efficiency of lignocellulosic fermentation processes.publishedVersio

Combined analytical strategies for chemical and physical characterization of tar from torrefaction of olive stone

The advance in analytical methodology is critical for progress in 1) biorefinery and 2) torrefaction product commercialization. The chemical characterisation of torrefaction liquid and concentrated tar produced by Arigna Fuels’ pyrolysis plant allowed identification of polar, volatile, non-volatile compounds, species containing organically bound sulphur and nitrogen heteroatoms. The results suggest that only combined use of ion chromatography with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry, and 1H-13C HS-QC can provide comprehensive information on sugar-like material and lignin-derived compounds. Due to the technical robustness and short analysis time, Fourier Transform Ion Cyclotron Resonance Mass Spectrometer was found to be a promising tool for tar analysis containing heavy molecular compounds. Importantly from a technological standpoint, the presence of aromatic and saturated compounds in both liquid and concentrated tar samples indicated the predominance of lignin-derived compounds over products originating from cellulose and hemicellulose polymers.publishedVersio

Combined analytical strategies for chemical and physical characterization of tar from torrefaction of olive stone

The advance in analytical methodology is critical for progress in 1) biorefinery and 2) torrefaction product commercialization. The chemical characterisation of torrefaction liquid and concentrated tar produced by Arigna Fuels’ pyrolysis plant allowed identification of polar, volatile, non-volatile compounds, species containing organically bound sulphur and nitrogen heteroatoms. The results suggest that only combined use of ion chromatography with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry, and 1H-13C HS-QC can provide comprehensive information on sugar-like material and lignin-derived compounds. Due to the technical robustness and short analysis time, Fourier Transform Ion Cyclotron Resonance Mass Spectrometer was found to be a promising tool for tar analysis containing heavy molecular compounds. Importantly from a technological standpoint, the presence of aromatic and saturated compounds in both liquid and concentrated tar samples indicated the predominance of lignin-derived compounds over products originating from cellulose and hemicellulose polymers.publishedVersio

Evaluation of Dynamic Models of Distillation Columns with Emphasis on the Initial Response

The flow dynamics (tray hydraulics) are of key importance for the initial dynamic response of distillation columns. The most important parameters are the liquid holdup, the liquid hydraulic time constant and the vapor constant representing the initial effect of a change in vapor flow on liquid flow. In the paper we present methods for determining these parameters experimentally, and compare the results with estimates from available correlations such as the Francis Weir formula

CONTROLLING FLUE GAS TEMPERATURE FROM FERRO SILICON SUBMERGED ARC FURNACES (SAF) USING FLUE GAS RECIRCULATION (FGR)

Flue gas Recycling (FGR) is a well-known method for NOx reduction. A feasibility study is presented on the potential use of FGR in ferro-silicon production. The aim of the study is to illustrate how recycling of flue gas into the furnace for temperature control will affect local temperatures and NOx formation in the furnace hood (the flue gas combustion zone) of a conventional furnace design. Computational fluid dynamic (CFD) simulations using a generic model of a submerged arc furnace (SAF) developed in previously NFR financed projects like ProMiljø are performed. The SAF model consists of seven charging pipes, three electrodes and one flue gas stack. ANSYS FLUENT was used for modelling the interaction between process gas, ambient air, and flue gas. The simulation results show that introduction of recirculated flue gas affects the peak temperatures since the reduced oxygen concentration of flue gas significantly reduce the reaction rates compared to injection of air. A corresponding effect on NOx formation has been demonstrated, results indicate an order of magnitude reduction in NOx formation when recirculated flue gas ( 6vol% O2) is used in the combustion zone instead of air (21vol% O2). Simulations of the rapid increase in NOx production during an avalanche within the furnace is simulated using theoretical flow profiles. The effects of 1) recirculated flue gas, 2) rapid increase in the process gases from charging bed (burst), and 3) effect of radiation on NOx have been studied. The study showed that FGR has significant effect on NOx reduction. The study also showed that accounting for radiation is very relevant for an accurate estimation of NOx. The formation of process gas burst through a charging surface increase the rate of NOx formation

CONTROLLING FLUE GAS TEMPERATURE FROM FERRO SILICON SUBMERGED ARC FURNACES (SAF) USING FLUE GAS RECIRCULATION (FGR)

Flue gas Recycling (FGR) is a well-known method for NOx reduction. A feasibility study is presented on the potential use of FGR in ferro-silicon production. The aim of the study is to illustrate how recycling of flue gas into the furnace for temperature control will affect local temperatures and NOx formation in the furnace hood (the flue gas combustion zone) of a conventional furnace design. Computational fluid dynamic (CFD) simulations using a generic model of a submerged arc furnace (SAF) developed in previously NFR financed projects like ProMiljø are performed. The SAF model consists of seven charging pipes, three electrodes and one flue gas stack. ANSYS FLUENT was used for modelling the interaction between process gas, ambient air, and flue gas. The simulation results show that introduction of recirculated flue gas affects the peak temperatures since the reduced oxygen concentration of flue gas significantly reduce the reaction rates compared to injection of air. A corresponding effect on NOx formation has been demonstrated, results indicate an order of magnitude reduction in NOx formation when recirculated flue gas ( 6vol% O2) is used in the combustion zone instead of air (21vol% O2). Simulations of the rapid increase in NOx production during an avalanche within the furnace is simulated using theoretical flow profiles. The effects of 1) recirculated flue gas, 2) rapid increase in the process gases from charging bed (burst), and 3) effect of radiation on NOx have been studied. The study showed that FGR has significant effect on NOx reduction. The study also showed that accounting for radiation is very relevant for an accurate estimation of NOx. The formation of process gas burst through a charging surface increase the rate of NOx formation.publishedVersio